1. Field of the Invention
The present invention relates to a tilt steering apparatus comprising a tilt adjustment mechanism in which tilt lock is established only when an oscillation-free end of an operating arm portion of a tilt operating lever is positioned toward a steering wheel side; even when the tilt operating lever is oscillated to the steering wheel side, the tilt operating lever is prevented from returning under its own weight, thereby preventing it from being difficult to operate.
2. Description of the Related Art
Steering apparatuses commonly comprise a tilt mechanism provided as a means for facilitating movement of a steering wheel to the optimum driving position in terms of comfort for a driver. This mechanism allows the steering wheel to be moved up and down to the optimum position for drivers of a range of body sizes. The tilt steering operation can be performed by oscillating a tilt operating lever that is normally tightened (locked) to a release side (side to which the tilt operating lever is loosened).
The tilt steering operation for adjusting the steering wheel position can only be performed when the tilt operating lever is released, the steering wheel position being reliably fastened as a result of the tilt operating lever being set to a fasten side (being tightened). Tilt mechanisms of improved usability in which the steering wheel adjustment performed subsequent to the tilt operating lever being untightened and positioned to the tilt operating lever release side and the angle of the tilt operating lever being held and then fastened at the release side in order to perform the abovementioned steering wheel tilt adjustment can be performed by a driver using both hands or legs are available. In addition, tilt mechanisms of a type in which, as operating means thereof, the tilt lock is able to be released only when an oscillation-free end of an operating arm portion of the tilt operating lever is positioned toward the steering wheel side have increased in recent years.
However, in tilt mechanisms of a type in which the tilt lock is released only when an oscillation-free end of an operating arm portion of the tilt operating lever is positioned toward the steering wheel side such as described above, the tilt operating lever, under its own weight, oscillates naturally to the fixed (lock) side of the tilt operation and attempts to return to the lock side position.
When this occurs, the driver must hold and support the steering wheel with one hand while holding the abovementioned tilt operating lever with the other—an extremely troublesome tilt operation that places a significant burden on the driver. The invention of Japanese Unexamined Patent Application Publication No. 2005-199733 was proposed with a view to preventing this kind of undesirable state. Japanese Unexamined Patent Application Publication No. 2005-199733 describes a mechanism comprising a spring affixed with displaced phase (angle) to the tilt operating lever in which moment is generated by the spring on the tilt operating lever in the fasten direction at a position on the fasten side of the tilt operating lever, and zero moment is generated on the tilt operating lever by the spring when the tilt operating lever is released.
According to the configuration described above, because tilt operating lever loosening at the tilt operating lever fasten side is prevented by the moment generated in the fasten direction and, in addition, because there is zero moment generated when the tilt operating lever is set to the release side, the tilt operating lever does not rotate in the fasten direction. The cited reference also describes how, because the magnitude of the moment applied to the tilt operating lever by the spring gradually reduces from the fasten side toward the release side as the tilt operating lever is rotated from the fasten side to the release side, the tilt operating lever can be operated using minimal force.
However, the following problems are inherent to the invention of Japanese Unexamined Patent Application Publication No. 2005-199733. First, while zero moment is generated by the spring when the tilt operating lever is set to a position on the release side (lock release side), the angle of the tilt operating lever at lock release cannot be maintained under its own weight and the tilt operating lever rotates slightly in the fasten direction (lock direction) whereupon, as a result, with the angle of the tilt operating lever slightly toward the fasten side, the tilt steering operation is slightly harder.
Furthermore, while there is zero moment finally applied to the tilt operating lever at the release side (lock release side), because the rotational moment generated by the spring is always applied in the fasten direction from the fasten side to the release side, the force for operating the tilt operating lever is increased as a result of a spring being affixed by the amount of this spring moment and, when the tilt operating lever is rotated from the fasten side to the release side, the moment applied by the spring acts constantly in the reverse direction to the direction in which the force of the hands is applied.